This invention is concerned with a composite material composed essentially of an ion-exchanged, synthetic, crystalline mica and an organic resin. It is further concerned with the production of such composite in the form of a sheet or board that is relatively strong, is fire-retardant, and can be punched and/or drilled.
U.S. Pat. No. 4,239,519 (Beall et al.) describes the production of gels from a synthetic, lithium and/or sodium, water-swelling mica. It further describes producing papers and films from such gels. The method described for gel production comprises three basic steps:
(1) a fully or predominantly crystalline body is formed (commonly a glass-ceramic body) containing crystals consisting essentially of a lithium and/or sodium, water-swelling mica selected from the group of fluorhectorite, hydroxyl hectorite, boron fluorphlogopite, hydroxyl boron phlogopite, and solid solutions among those and between those and other structurally-compatible species selected from the group of talc, fluortalc, fluoropolylithionite, polylithionite, phlogopite, and fluorophlogopite;
(2) the body is contacted with a polar liquid, normally water, to cause swelling and disintegration of the body accompanied with the formation of a gel; and
(3) the solid:liquid ratio of the gel is adjusted to a desired level depending upon the product to be prepared therefrom.
Gels formed in this manner are broken and flocculated by contact with a source of a large exchangeable cation, usually potassium (K.sup.+). The large cation replaces lithium and/or sodium ions on the silicate surfaces.
Efforts were made to form board by flocculating the mica gel by ion exchange, vacuum draining the floc material, and pressing the filter cake. The pressed material was observed to be rather weak and porous. However, certain properties, such as electrical properties, were of interest. Therefore, it became desirable to somehow modify the cake to impart strength and eliminate porosity without unduly diminishing other properties.